Direct evidence of V-V dimers existing in the metallic-phase of VO₂

We utilized EXAFS at the V K-edge to measure V-V distances of VO₂ from 40 to 110 °C. The DC resistance was simultaneously measured with EXAFS. Results showed structural and metal-insulator phase transitions at 70 °C and 75 °C, respectively. Below 70 °C, the interatomic distances of V-V pairs were around 2.65 Å and 3.01 Å in the insulating phase, changing to about 2.85 Å and 3.02 Å in the metallic phase, respectively. V-V dimers persisted even at 110 °C. VO₂ maintained the M1 phase from 40 to 110 °C, with some changes in local structural properties like distances and Debye-Waller factors of atomic pairs with temperature.